1. Field of the Invention
The present invention relates to a smoke detector capable of optically detecting smoke and contaminants floating in the air.
2. Description of the Related Art
Conventionally, there has been used a smoke detector for detecting smoke so as to prevent and identify a fire, or for detecting contaminants (dust or the like) so as to preserve an environment in a semiconductor manufacturing plant, a food factory, or the like (so-called clean room or the like).
Among various smoke detectors, there is an optical smoke detector for optically detecting smoke and contaminants contained in the air (hereinafter referred to as “smoke or the like”).
The optical smoke detector generally detects smoke or the like in a manner that a light receiving section receives scattered light generated in a smoke detecting section when light emitted from a light emitting section is scattered due to particles of the smoke or the like. However, light receiving sensitivity of the light receiving section may be reduced due to contamination or the like. In view of the above, as described in, for example, Japanese Patent Application Laid-open No. Hei 7-151680 (hereinafter referred to as “Patent Literature 1”), a test light emitting section for emitting test light is provided separately, and received light intensity of the test light at the light receiving section is measured, to thereby correct the light receiving sensitivity of the light receiving section based on the light intensity thus measured, and to output an alarm indicating abnormality when the light intensity becomes equal to or lower than a predetermined value (see paragraphs and in the specification and FIG. 23 of Patent Literature 1).
However, as in the case of the above-mentioned smoke detector described in Patent Literature 1, in a case of detecting the reduction in light receiving sensitivity of the light receiving section based on decrease in received light intensity at the light receiving section, the reduction in light receiving sensitivity is detected by measuring an amount of decrease from the normal received light intensity. Accordingly, the reduction in light receiving sensitivity is detected based on the decreasing received light intensity of the test light having much higher light intensity than the scattered light. Consequently, there arises a problem in that the reduction in light receiving sensitivity cannot be detected with high accuracy.
Further, in the case of the above-mentioned smoke detector described in Patent Literature 1, the test light having much higher light intensity than the scattered light is caused to enter a light receiving element at the front thereof (see paragraph of Patent Literature 1). Even when the contamination or the like in the light receiving section is so serious as to hinder the entrance of the scattered light, the entrance of the test light may be less affected by the contamination or the like. To avoid this situation, a strict threshold value may be set at the time of the test, but as a result, the course of the contamination or the like cannot be monitored.